As the display technique has progressed, more and more active matrix organic light emitting diode (AMOLED) display panels are going to enter the market. Compared with a conventional thin film transistor liquid crystal display (TFT LCD) panel, the active matrix organic light emitting diode display panel has the advantages of low energy consumption, low production cost, self light emission, wide viewing angle, high response speed and the like. At present, the active matrix organic light emitting diode display panel has already started replacing a conventional LCD display screen gradually in the fields of cellphone, PDA, digital camera and the like. Unlike a TFT LCD, which controls brightness with a stable voltage, AMOLED is current-driven and needs a stable current to control light emission.
As shown in FIG. 1, an existing pixel circuit driving an OLED to emit light comprises a drive transistor M1, a switch transistor M2, a storage capacitor C, and a light emitting device OLED, wherein a gate electrode of the drive transistor M1 is connected with a drain electrode of the switch transistor M2 and one end of the storage capacitor C, a source electrode thereof is connected with a high-voltage signal end VDD, and a drain electrode thereof is connected with the other end of the storage capacitor and one end of the light emitting device OLED. A gate electrode of the switch transistor M2 is connected with a scan signal end Gate, and a source electrode thereof is connected with a data signal end Data. The other end of the light emitting device OLED is connected with a low-voltage signal end VSS. When the drive transistor M1 drives the light emitting device OLED to emit light, a driving current is controlled jointly by the high-voltage signal end VDD, the data signal end Data and the drive transistor M1. Because a luminous brightness of the OLED is quite sensitive to a change in the driving current thereof, and the drive transistor M1 may not be made completely consistent in a fabrication process. In addition, due to reasons such as a process flow and device aging, as well as a temperature change in a working process, a threshold voltage Vth of the drive transistor M1 in each pixel circuit is non-uniform, which causes a change to the current flowing through each pixel point OLED, such that a display brightness is non-uniform, thereby affecting a display effect of the whole image.
Accordingly, a problem to be solved by a person skilled in the art is how to eliminate the influence of the change in the threshold voltage of the drive transistor in the pixel circuit on the luminous brightness of the light emitting device, to ensure the uniformity of the current for driving the light emitting device OLED so as to ensure the quality of a display frame.